Real-time location or position determinations for objects have become increasingly beneficial across a wide spectrum of applications. Real-time locating systems (RTLS) are used and relied on for tracking objects, such as portable devices, in many realms including, for example, automotive, storage, retail, security access for authentication, and security access for authorization.
One conventional RTLS system in the automotive realm includes a transceiver or master controller located within a vehicle and capable of communicating via radio frequency with a portable device. The master controller may monitor the signal strength of the communications between itself and the portable device, and use this monitored information as a basis for determining a location of the portable device relative to the vehicle. This type of RTLS system, however, is often inaccurate, primarily because factors other than distance, such as interference, can affect signal strength. For instance, if the signal strength drops due to interference rather than an actual increase in distance, the transceiver may incorrectly determine the portable device is located farther away than its actual distance or a distance that would have been determined without the interference.
Numerous technologies have centered around using signal strength of communications between a transmitter and a receiver to determine location information. However, these technologies often fail to provide accurate location information under varied circumstances. For instance, in addition to the interference issue described above, resource allocation in the portable device can adversely affect the ability to utilize signal strength as a basis for determining location information. For instance, in the context of Bluetooth communication systems, the portable device is often limited by its resources to a select number of concurrent Bluetooth operations. If the portable device is a phone that is attempting to make a Hands-Free Profile (HFP) voice connection, while at the same time trying to determine the phone's position relative to the vehicle, the portable device may prioritize the HFP connection over connections that facilitate determining the phone's position. This prioritization may be the direct result of resource allocation in the portable device, and can adversely affect the ability to determine location information about the portable device relative to the vehicle. Measurement error is also often a significant source of error—signal strength, timing, and angles measured at different times may vary due to limitations of the instruments on the devices taking the measurements or because they were taken at different times.